1. Technical Field
This invention relates to fuzes for munitions such as grenades, and more particularly to a fuze having a centrifugal lock for allowing arming of the fuze only when its associated munition is deployed from an airborne projectile.
2. Discussion
Fuzes are used in a variety of applications with various forms of munitions to arm a munition so that the munition can be detonated. With grenades adapted for airborne deployment, such as from artillery shells, such grenades typically employ an arming screw having a firing pin portion. A drag ribbon is typically attached to one end of the arming screw. Arming of the fuze is accomplished when the fuze and its associated munition are deployed from an airborne rocket or artillery shell and the munition begins falling toward the Earth while it is spinning at a very high rate. During this time the drag ribbon causes the arming screw to be unscrewed from an interior inertia weight. As the arming screw becomes fully unscrewed from the inertia weight other components within the fuze are allowed to move to place a detonator device in line with the firing pin of the arming screw. Upon impact with a target or ground surface, the inertia weight assists in driving the tiring pin into the detonator to detonate the main explosive charge of the munition.
One problem with the above-described fuze mechanism is that unintentional arming of the fuze may occur under certain conditions. For example, if the munitions housed within an artillery shell carried on board a war ship are released therefrom, such as if the ship is struck by an enemy missile, the potential exists for the munitions to roll around on the deck of the ship. During this time, there is the possibility that the arming screw of a fuze mechanism of one or more of the munitions may become unthreaded from its associated inertia weight. In this instance, any such fuze mechanism having its arming screw fully unthreaded would be placed in an armed yet undetonated condition.
Thus, it is a principal object of the present invention to provide a fuze for a munition which prevents arming of the munition unless the munition is deployed from an airborne rocket or artillery shell. More specifically, it is an object of the present invention to provide a fuze mechanism which cannot be placed in an armed condition merely by the munition rolling around on a ship deck, ground surface or other like, relatively flat area.
It is still a further object of the present invention to provide a fuze for a munition which can only be armed by placing the munition in a highly rapidly spinning condition, such as when the munition is deployed from an airborne rocket or artillery shell, and where the rate of spin of the munition is on the order of several thousand rpm.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.
The above and other objects are provided by a fuze mechanism in accordance with preferred embodiments of the present invention. The fuze mechanism includes an arming screw and a centrifugal locking mechanism. The centrifugal locking mechanism engages a portion of the arming screw and prevents rotation of the arming screw unless the fuze mechanism is spinning at a rate sufficiently high so as to generate a predetermined degree of centrifugal force to release the centrifugal locking mechanism from engagement with the arming screw. As a result, the arming screw can only begin to unscrew from the fuze mechanism when the fuze mechanism and its associated munition is placed in a highly spinning condition, such as that which occurs when the fuze and its munition are deployed from an airborne rocket or artillery shell and the rate of spin is typically several thousand rpm or greater.
In one preferred embodiment the centrifugal locking mechanism comprises a pair of locking members and the arming screw comprises a keyed portion. Each of the locking members further includes cutouts formed in accordance with the keyed portion of the arming screw such that the locking members can engage the keyed portion securely. A pair of biasing elements are also used to hold the locking members in engagement with the keyed portion of the arming screw. The biasing elements provide a biasing force sufficient to hold the locking members securely against the keyed portion of the arming screw when the fuze is not spinning or is spinning at a low rate of rotation, but which allow centrifugal force acting on the locking members to urge them out of engagement with the keyed portion of the arming screw when the fuze reaches a high rate of spin that only occurs during airborne deployment of munitions from rockets or artillery shells. As such, the locking members are not able to be disengaged from the keyed portion of the arming screw in the event that the fuze and its associated munition is released onboard a ship deck or any other relatively flat surface where it is able to roll.
The centrifugal locking mechanism thus provides an effective yet relatively simple means for preventing rotation of the arming screw except when the fuze is deployed from an airborne rocket or artillery shell. Importantly, the centrifugal locking mechanism does not add significantly to the cost of the fuze or require enlarging the dimensions of the fuze or significantly increase its complexity.